Process for the manufacture of semifinished products of zinc



United States Patent 3,340,715 PROCESS FOR THE MANUFACTURE OF SEMI- FINISHED PRODUCTS OF ZINC Hans Bothmann, Aachen, and Ernst Dorn and Werner Krauss, Duisburg-Hamborn, Germany, assignors to Aktiengesellschaft fur Zinkindustrie vorm. Wilh. Grillo, Duisburg-Hamborn, Germany No Drawing. Filed Mar. 26, 1963, Ser. No. 267,956 Claims priority, application Germany, Mar. 30, 1962,

A 39,8 19 Claims. (Cl. 72-364) This invention relates to a process for the manufacture of semi-finished products of zinc having improved deepdrawing properties.

The manufacture of semi-finished products of zinc, particularly strips and sheet, having adequate technological properties which are invariable for extended periods of storage, especially invariable deep-drawing properties, has been hardly possible up to the present. The technological properties are primarily changed due to crystal recovery or recrystallization occurring already at very low temperatures which partially may be as low as normal room temperatures. A further cause of variations of the technological properties resides in the fact that zinc falls into the group of hexagonally crystallizing metals and substantially only the base face is effective as the sliding face.

It is known from the crystallographic processes occurring in cold working that the latter is dependent either on sliding or on twin formation in the crystal. The extent to which pure sliding or pure twin crystal formation or a combination of these two processes plays a part in cold working is different from metal to metal and the knowledge so far available hereon is relatively indistinct. Especially in the case of zinc it has not become known up to the present that the presence of twin crystals may exert a very substantial influence on the workability of zinc. The reason hereof may partially be the fact that a twin crystal structure in zinc is very labile with respect to its thermal stability. In case of the previously known zinc grades as conventionally used for the manufacture of semi-finished products, crystal recovery or recrystallization occur already at very low temperatures and variations of crystal structures by disappearance of twin crystals appear in most cases at moderately elevated room temperatures. It has now been found that in the case of zinc a very significant interrelation which was fully unknown up to the present but which is very important with respect to its technological effect is existing between a twin crystal structure and the workability and that it is possible to stabilize a twin structure with respect to its thermal stability.

It is an object of this invention to provide a process for the manufacture of semi-finished products of zinc having improved deep-drawing properties with the use of conventional working methods, the process comprising using as the starting material zinc alloyed with specific alloying additions which increase the recrystallization temperatures of fine zinc without affecting the workability and effecting the shaping to semi-finished product-s suitable for further processing first in conventional manner as described, for example, by A. Burkardt in Technologie der Zink-Legierungen by hot working and effecting the last processing step by cold working.

In accordance with the invention, the alloying additions are preferably added to the zinc in amounts of from 0.004 to 0.015%, it being possible for the addition to consist of a combination of suitable addition metals or of a single metal.

Hot working is preferably effected with an average reduction per pass of about 10 to 50% and reductions of 25 to 30%. In case of the last cold pass the reduction is then less than 10% and preferably only 4 to 7%.

For the manufacture of deep-drawn articles from zinc 3,340,715 Patented Sept. 12, 1967 strips, it was usual up to the present to use fine zinc having a purity of 99.995% and containing lead, cadmium, tin or iron as contaminations. Strips of this kind are generally rolled down to thicknesses of 1 mm. and down to 0.1 mm. and then processed to deep-drawn articles of cup-like shape.

When drawing these articles, it was observed that satisfactory and poor workabilities alternate despite the fact that chemically the compositions of the material were identical and also the mode of processing was not different. Strips obtained from the same batch had partially satisfactory deep-drawing properties and partially extremely poor deep-drawing properties. Furthermore, it was found that strips which immediately upon their manufacture had satisfactory deep-drawing properties underwent changes after more or less extended periods of storage to an extent such that they lost their capability of being cupped.

Experiments carried out by applicants have shown that satisfactory deep-drawing properties are obtained in the manufacture of semi-finished products of zinc if twin crystal structures are present in the zinc strips as evidenced by metallographic tests. In the absence of twin crystal structures, the deep-drawing properties are lost to an extent such that further use for deep-drawing purposes is impossible. It appeared that the thermal stability of the twin structure is very poor. Zinc strips of known type containing twin structures undergo a change of the crystal structure by disappearance of the twin crystals already after storage periods of a few days or, in case of minor increases in temperature, already after a short period of time. The deep-drawing properties of the material immediately change as the twin crystals disappear. If special alloying additions in accordance with the invention are added to the zinc, it is possible to stabilize the twin structure. Particularly suitable alloying additions are metals such as copper, titanium, aluminum, iron, magnesium as well as manganese, chromium and nickel alone or in combinations. In contrast, the known contaminations of highly pure zinc alloys as mentioned above, i.e., tin and lead, are no suitable stabilizers for the twin crystal structure. The stabilizer can be cadmium.

As mentioned above, it is possible in accordance with one feature of the invention to use the alloying additions in amount-s which are in the order of magnitude of contaminations so that the starting material used may also be a fine zinc. It is particularly surprising that the alloying additions used in accordance with the invention are effective in very small amounts.

Example 1 For comparative purposes, a fine zinc was first processed in conventional manner:

Refined zinc having a purity of 99.995 and analyzing -0.00l% Pb, 0.001% Cd, 0.001% Sn and 0.0008% Fe was cast in normal manner to form a rolling ingot of mm. thickness which was rolled down, beginning at,

ordinary rolling temperatures of 200 C., to 0.3 mm. thickness, the reductions from pass to pass being within the limits of 7 to 25% when rolling down to 3 mm. The passes when rolling down from 3 mm. to 0.3 mm. were as follows:

strip was allowed to cool completely and then rolled cold from 0.32 to 0.30 mm. Thus, the last pass is a cold pass with a reduction of only 4.57%. The structure obtained in this manner and containing a great number of twin crystals was found to have extremely satisfactory deepdrawing properties. However, if this strip was kept for a few hours at moderate temperatures up to about 3040 C., these twin crystals disappeared. A normal recrystallization structure and very poor deep-drawing characteristics were re-established.

If specific alloying elements are added to the refined zinc in amounts which are sufficiently small that the workability is not varied or changed to an insignificant degree only, then the transition from a twin structure into a recrystallization structure can be shifted to substantially higher temperatures so that the twin structure which is so important .for the deep-drawing property can be preserved also at higher temperatures.

For this purpose, the above-mentioned fine zinc was alloyed with 0.001% of Al, 0.002% of Fe, 0.001% of Cu and 0.00004% of Mg and 0.003% of Cd and rolled down in a cold pass with a reduction of between 4.5 and 7% in the manner described above to obtain a twin crystal structure. The material obtained after rolling had again a pronounced twin structure. This twin structure was found to be absolutely stable when annealing the material for 24 hours at 80 C. or for more than 6,000 hours at 50 C.

The experiment described above was repeated with the appropriate amount of each of the alloying elements alone and with different amounts of the components of the combination with the combined metal additions being in the same order of magnitude as in the experiment described above. In all cases, a strip was obtained which had satisfactory capability of being cupped even after storage for months.

Example 2 A zinc-base alloy containing 0.6% Cu and 0.12% Ti was rolled down hot to 0.74 mm. thickness beginning at 250 C. and using reductions of 20 to 30% between two successive passes. After hot rolling, the material was annealed for 2 hours at 400 C., which resulted in an absolutely clear recrystallization structure. Part of this annealed material was then rolled down 4% and 7% in a cold pass. The material clearly showed twin structure while the material which had been rolled down hot and annealed showed recrystallization rather than twin struc ture. Both of the materials were subjected to the cupping test which clearly showed that only the material having twin structure was capable of being deep-drawn while the material which had only been annealed and which had the recrystallization structure did not pass the cupping test at all.

Example 3 Example 2 was repeated except that the amount of copper was about 1.5% and that of titanium 0.5%. The same effect as in Examples 1 and 2 was obtained. This effect was unchanged if, for example, an alloying addition comprising 0.5% of copper and about 0.2% titanium was used.

What is claimed is:

1. A process for the manufacture of semi-finished products of zinc having improved deep-drawing properties with the use of conventional working methods, which comprises using as the starting material fine zinc admixed with alloying additions which increase the recrystallization temperatures of the fine zinc without impairing the workability and effecting the working into a semiproduct suitable for further processing by first subjecting the material to conventional hot working involving rolling, drawing or compressing and then carrying out the last processing step by cold working to a reduction of less than 10%.

2.. A process according to claim 1, wherein said hot working is effected with passes involving reductions of 10 to 50%.

3. A process according to claim 2, wherein said reduction in said cold pass is 4 to 7%.

4. A process according to claim 1, wherein said alloying addition is copper.

5. A process according to claim 1, wherein said alloying addition is titanium.

6. A process according to claim 1, wherein said alloying addition is aluminum.

7. A process according to claim 1, wherein said alloying addition is iron.

8. A process according to claim 1, wherein said alloying addition is manganese.

9. A process according to claim 1, wherein said alloying addition is cadmium.

10. A process according to claim 1, wherein said alloying addition is magnesium.

11. A process according to claim 1, wherein said alloying addition is a mixture of metals.

12. A process according to claim 11, wherein said mixture is selected from the group consisting of mixtures comprising two metals and mixtures comprising more than two metals.

13. A process according to claim 11, wherein said mixture contains metals selected from the group consisting of aluminum, iron, copper, magnesium and cadmium.

14. A process according to claim 11, wherein said mixture is an alloy consisting of copper and titanium.

15. Process according to claim 1, said semi-finished products having a stabilized twin crystal structure and being stabilized against recrystallization by said alloying additions.

16. Process according to claim 1, wherein said alloying addition is selected from the group consisting of copper, titanium, aluminum, iron, magnesium, manganese, chromium, nickel, cadmium, and mixtures thereof.

17. Process for the manufacture of drawn zinc products which comprises subjecting to drawing a semi-finished product according to claim 1.

18. Process for the manufacture of drawn zinc products which comprises subjecting to drawing a semi-finished product according to claim 1.

19. Process for the manufacture of drawn zinc products which comprises subjecting to drawing a semi-finished product according to claim 16.

References Cited UNITED STATES PATENTS 2,060,919 11/1936 Anstey et al. -178 2,448,169 8/1948 Boyle et al 148-115 3,113,053 12/1963 Zvanut 1481l.5 3,146,098 4/1964 Saarivirta et al. 148ll.5

CHARLES W. LANHAM, Primary Examiner,

L. A, L RSON. Assistant Examiner, 

1. A PROCESS FOR THE MANUFACTURE OF SEMI-FINISHED PRODUCTS OF ZINC HAVING IMPROVED DEEP-DRAWING PROPERTIES WITH THE USE OF CONVENTIONAL WORKING METHODS, WHICH COMPRISES USING AS THE STARTING MATERIAL FINE ZINC ADMIXED WITH ALLOYING ADDITIONS WHICH INCREASE THE RECRYSTALLIZATION TEMPERATURES OF THE FINE ZINC, WITHOUT IMPARING THE WORKABILITY AND EFFECTING THE WORKING INTO A SEMIPRODUCT SUITABLE FOR FURTHER PROCESSING BY FIRST SUBJECTING THE MATERIAL TO CONVENTIONAL HOT WORKING INVOLVING ROLLING, DRAWING OR COMPRESSING AND THEN CARRYING OUT THE LAST PROCESSING STEP BY COLD WORKING TO A REDUCTION OF LESS THAN 10%. 